Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $131.49   10.157%   $144.8454   $144.85   $144.85   $144.80  
  Purchase #2 $5.66   8.337%   $6.1319   $6.13   $6.15   $6.10  
  Purchase #3 $86.28   13.556%   $97.9761   $97.98   $98.00   $98.00  
  Purchase #4 $14.46   8.775%   $15.7289   $15.73   $15.75   $15.70  
  Purchase #5 $61.52   11.850%   $68.8101   $68.81   $68.80   $68.80  
  Purchase #6 $60.45   10.859%   $67.0143   $67.01   $67.00   $67.00  
  Purchase #7 $57.55   10.752%   $63.7378   $63.74   $63.75   $63.70  
  7 purchase totals = $417.41       $464.2445   $464.25   $464.30   $464.10